推理是「使用理智从某些前提产生结论」的行动。以下三种推理是属于哲学、逻辑、心理学和人工智能等学门所感兴趣的领域。

有两种主要的方式可以达成推理的结论：其一为演绎推理(Deductive Reasoning)，给出正确的前提，就必然推出结论（结论不能为假）。演绎推理无法使知识扩增，因为结论自包含于前提之内。逻辑学中有名的三段论（syllogism）就是典型的例子：

另一方面，在归纳推理（Inductive Reasoning）当中，当前提为真时，可推出某种机率性的结论。归纳推理可以扩展知识，因为结论比前提包含更多的信息。大卫·休谟（David Hume）曾举出一个归纳推理的范例：

Inference is the act or process of deriving logical conclusions from premises known or assumed to be true. The laws of valid inference are studied in the field of logic.

Alternatively, inference is defined as the non-logical, but rational means, through observation of patterns of facts, to see new meanings and contexts for understanding indirectly. Of particular use to this application of inference are anomalies and symbols. Inference, in this sense, does not draw conclusions but opens new paths for inquiry. (See second set of examples.) In this definition of inference, there are two types of inference: inductive inference and deductive inference. Unlike the definition of inference in the first paragraph above, meaning of word meanings are not tested but meaningful relationships are articulated.